Genotyping-by-sequencing-based identification of Arabidopsis pattern recognition receptor RLP32 recognizing proteobacterial translation initiation factor IF1

Pattern-triggered immunity (PTI) is a central component of plant immunity. Activation of PTI relies on the recognition of microbe-derived structures, termed patterns, through plant encoded surface-resident pattern recognition receptors (PRRs). We have identified proteobacterial translation initiation factor 1 (IF1) as an immunogenic pattern that triggers PTI in Arabidopsis thaliana and some related Brassicaceae species. Unlike most other immunogenic patterns identified, IF1 elicitor activity cannot be assigned to a small peptide epitope, suggesting that tertiary fold features are required for IF1 receptor activation. We have deployed natural variation in IF1 sensitivity to identify leucine-rich repeat (LRR) receptor-like protein 32 (RLP32) as the corresponding Arabidopsis receptor using a restriction site-associated DNA sequencing (RAD-seq) approach. Transgenic expression of RLP32 confers IF1 sensitivity to rlp32 mutants, IF1-insensitive Arabidopsis accessions and IF1-insensitive Nicotiana benthamiana. RLP32 binds IF1 specifically and forms complexes with LRR receptor kinases SOBIR1 and BAK1 to mediate signaling. Similar to previously identified PRRs RLP32 confers resistance to Pseudomonas syringae infection, highlighting an unexpectedly complex array of bacterial pattern sensors within a single plant species.